It is a popular belief that the primary etiological factor in muscle-contraction headache is sustained muscle tension. However, studies investigating this relationship have yielded somewhat inconsistent results and the relatively small amount of variance in headache activity accounted for by muscular activity suggests that additional etiological factors may be involved. This proposed project involves four studies designed to investigate the role of restricted blood flow (extra-cranial cephalic vasoconstriction) at the site of the muscle-contraction headache. In the first study, subjects with and subjects without frequent muscle-contraction headaches will be compared on six extracranial cephalic blood flow measures (using reflectance photophethysmography) during rest, two different types of stressors (physical and cognitive), and during post-stress adaptation. In the second study, subjects with frequent muscle-contraction headache will be assessed with the same six blood flow measures and during the same experimental conditions; however, they will be tested twice when they are experiencing a headache and twice when they are not experiencing a headache (in counter-balanced order). In the third study, subjects with and subjects without frequent muscle contraction headaches will be subjected to a long duration (1 hour) stressor while the same six cephalic blood flow measures are taken. Because this duration of stressor has been shown to precipitate a muscle-contraction headache in susceptible subjects, this study is designed to provide information on cephalic blood flow patterns before, during, and following headache. In the fourth study, subjects with frequent muscle-contraction headaches will be exposed to extracranial cephalic blood volume pulse biofeedback designed to facilitate their ability to produce dilation in arterioles at the site of the headache.